Java实现ZooKeeper的zNode监控
上一篇文章已经完成了ZooKeeper的基本搭建和使用的介绍,现在开始用代码说话。参考https://zookeeper.apache.org/doc/current/javaExample.html,但对场景和代码都做了简化,只实现基本的Watcher功能。
1 场景设计
目的是体验ZooKeeper的Watcher功能。程序监控ZooKeeper的/watcher节点数据变化,当创建或修改数据时,控制台打印当前的数据内容和版本号;当/watcher被删除时,程序退出。
/watcher的创建、修改和删除操作,使用控制台或zkui操作。
2 搭建Maven项目
代码相对比较简单,就不用SpringBoot这个大杀器了,使用一个普通的Maven项目即可。
ZooKeeper客户端使用官方提供的Java库,org.apache.zookeeper:zookeeper:3.5.5。日志框架使用习惯的slf4j+log4j2,ZooKeeper缺省使用的是log4jV1,因此在引入的时候需要excludes。另外,使用了lombok来简化一些代码。
以下是pom.xml的内容
4.0.0 tech.codestory.research zookeeper 1.0.0-SNAPSHOT org.apache.zookeeper zookeeper 3.5.5 log4j log4j org.slf4j slf4j-log4j12 org.apache.logging.log4j log4j-core 2.12.1 org.apache.logging.log4j log4j-api 2.12.1 org.apache.logging.log4j log4j-web 2.12.1 org.apache.logging.log4j log4j-slf4j-impl 2.12.1 org.slf4j slf4j-api 1.7.28 org.slf4j slf4j-ext 1.7.28 org.projectlombok lombok 1.18.8 provided
3 log4j2.xml
在项目的src/main/resources下创建一个文件log4j2.xml,内容为
4 创建ZooKeeper连接
创建连接代码比较简单,只需要创建ZooKeeper对象就行,
ZooKeeper构造函数的定义
/** *创建一个ZooKeeper客户端对象 *@paramconnectString逗号分隔的host:port字符串, *单点如127.0.0.1:2181, *集群如192.168.5.128:2181,192.168.5.129:2181,192.168.5.130:2181, *还可以指定根节点,如127.0.0.1:2181/foo/bar *@paramsessionTimeout毫秒为单位的超时时间 *@paramwatcherWatcher对象,用于接收MatcherEvent *@throwsIOException网络错误时抛出异常 *@throwsIllegalArgumentException如果Root路径设置错误 */ publicZooKeeper(StringconnectString,intsessionTimeout,Watcherwatcher) throwsIOException;
写一段测试代码,创建zk对象后判断某一个zNode是否存在。
publicclassZooKeeperWatcherimplementsWatcher{ /**ZooKeeper的客户端连接*/ ZooKeeperzk; publicZooKeeperWatcher(StringhostPort,StringzNode)throwsKeeperException,IOException{ zk=newZooKeeper(hostPort,3000,this); try{ Statexists=zk.exists(zNode,true); if(exists==null){ log.info(“{}不存在”,zNode) } }catch(InterruptedExceptione){ log.error("InterruptedException",e); } } }
运行这段代码,发现会抛异常
java.net.SocketException:Socketisnotconnected atsun.nio.ch.Net.translateToSocketException(Net.java:162)~[?:?] atsun.nio.ch.Net.translateException(Net.java:196)~[?:?] atsun.nio.ch.Net.translateException(Net.java:202)~[?:?] atsun.nio.ch.SocketAdaptor.shutdownInput(SocketAdaptor.java:400)~[?:?] atorg.apache.zookeeper.ClientCnxnSocketNIO.cleanup(ClientCnxnSocketNIO.java:198)[zookeeper-3.5.5.jar:3.5.5] atorg.apache.zookeeper.ClientCnxn$SendThread.cleanup(ClientCnxn.java:1338)[zookeeper-3.5.5.jar:3.5.5] atorg.apache.zookeeper.ClientCnxn$SendThread.cleanAndNotifyState(ClientCnxn.java:1276)[zookeeper-3.5.5.jar:3.5.5] atorg.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1254)[zookeeper-3.5.5.jar:3.5.5] Causedby:java.nio.channels.NotYetConnectedException atsun.nio.ch.SocketChannelImpl.shutdownInput(SocketChannelImpl.java:917)~[?:?] atsun.nio.ch.SocketAdaptor.shutdownInput(SocketAdaptor.java:398)~[?:?] ...4more NotYetConnectedException的字面意思是连接还没有创建好,网络搜索了一下,建立连接需要一些时间,创建zk对象后马上调用exists命令,这时候连接还没有创建好,就会抛异常。ZooKeeper在连接建立成功之后,会发送一个WatchedEvent事件,我们可以利用这个事件完成建立连接的过程。修改后的代码如下,顺便添加了slf4j-ext中的Profiler,用于记录所消耗的时间。 publicclassZooKeeperWatcherimplementsWatcher{ /**等待连接建立成功的信号*/ privateCountDownLatchconnectedSemaphore=newCountDownLatch(1); /**ZooKeeper的客户端连接*/ ZooKeeperzk; publicZooKeeperWatcher(StringhostPort,StringzNode)throwsKeeperException,IOException{ Profilerprofiler=newProfiler("连接到ZooKeeper"); profiler.start("开始链接"); zk=newZooKeeper(hostPort,3000,this); try{ profiler.start("等待连接成功的Event"); connectedSemaphore.await(); Statexists=zk.exists(zNode,true); if(exists==null){ log.info(“{}不存在”,zNode) } }catch(InterruptedExceptione){ log.error("InterruptedException",e); } profiler.stop(); profiler.setLogger(log); profiler.log(); } /**收到ZooKeeper的WatchedEvent*/ @Override publicvoidprocess(WatchedEventevent){ log.info("event={}",event); if(Event.EventType.None.equals(event.getType())){ //连接状态发生变化 if(Event.KeeperState.SyncConnected.equals(event.getState())){ //连接建立成功 connectedSemaphore.countDown(); } } } }
修改代码之后的执行记录日志如下,可以看到等待连接成功的Event耗时9秒多。网络上有文章说关闭防火墙可以秒连,但我测试过,没发现有什么变化,使用systemctlstopfirewalld之后重新执行程序,仍然需要9秒多。
[INFO]-ZooKeeperWatcher.process(61)-event=WatchedEventstate:SyncConnectedtype:Nonepath:null [DEBUG]-ZooKeeperWatcher.log(201)- +Profiler[连接到ZooKeeper] |--elapsedtime[开始链接]78.912milliseconds. |--elapsedtime[等待连接成功的Event]9330.606milliseconds. |--Total[连接到ZooKeeper]9409.926milliseconds. [INFO]-ZooKeeperWatcher.readNodeData(95)-/watcher不存在
5 读取WatchedEvent
前面的代码,只是处理了建立连接成功时的Event,下面再来看看读取数据的过程。关键代码如下:
if(Event.EventType.NodeDataChanged.equals(event.getType()) ||Event.EventType.NodeCreated.equals(event.getType())){ Stringpath=event.getPath(); if(path!=null&&path.equals(zNode)){ //节点数据被修改 readNodeData(); } } /**读节点数据*/ privatevoidreadNodeData(){ try{ Statstat=newStat(); byte[]data=zk.getData(zNode,true,stat); if(data!=null){ log.info("{},value={},version={}",zNode,newString(data),stat.getVersion()); } }catch(KeeperExceptione){ log.info("{}不存在",zNode); }catch(InterruptedExceptione){ log.error("InterruptedException",e); } }
当接收到创建节点和修改节点的WatchedEvent,都会将数据读出并打印在控制台。
6 调整后的完整程序清单
对前面的代码做了部分调整,同时添加了退出系统的机制:节点被删除。
packagetech.codestory.zookeeper.watcher; importjava.io.IOException; importjava.util.concurrent.CountDownLatch; importorg.apache.zookeeper.*; importorg.apache.zookeeper.data.Stat; importorg.slf4j.profiler.Profiler; importlombok.extern.slf4j.Slf4j; /** *用于测试ZooKeeper的WatchedEvent用法 *@authorcodestory *@date2019/8/13 */ @Slf4j publicclassZooKeeperWatcherimplementsWatcher,Runnable{ /**等待连接建立成功的信号*/ privateCountDownLatchconnectedSemaphore=newCountDownLatch(1); /**退出系统的信号*/ staticIntegerquitSemaphore=Integer.valueOf(-1); StringzNode; ZooKeeperzk; publicZooKeeperWatcher(StringhostPort,StringzNode)throwsKeeperException,IOException{ this.zNode=zNode; Profilerprofiler=newProfiler("连接到ZooKeeper"); profiler.start("开始链接"); zk=newZooKeeper(hostPort,3000,this); try{ profiler.start("等待连接成功的Event"); connectedSemaphore.await(); }catch(InterruptedExceptione){ log.error("InterruptedException",e); } profiler.stop(); profiler.setLogger(log); profiler.log(); //先读当前的数据 readNodeData(); } /**收到ZooKeeper的WatchedEvent*/ @Override publicvoidprocess(WatchedEventevent){ log.info("event={}",event); if(Event.EventType.None.equals(event.getType())){ //连接状态发生变化 if(Event.KeeperState.SyncConnected.equals(event.getState())){ //连接建立成功 connectedSemaphore.countDown(); } }elseif(Event.EventType.NodeDataChanged.equals(event.getType()) ||Event.EventType.NodeCreated.equals(event.getType())){ Stringpath=event.getPath(); if(path!=null&&path.equals(zNode)){ //节点数据被修改 readNodeData(); } }elseif(Event.EventType.NodeDeleted.equals(event.getType())){ Stringpath=event.getPath(); if(path!=null&&path.equals(zNode)){ synchronized(quitSemaphore){ //节点被删除,通知退出线程 quitSemaphore.notify(); } } } } /**读节点数据*/ privatevoidreadNodeData(){ try{ Statstat=newStat(); byte[]data=zk.getData(zNode,true,stat); if(data!=null){ log.info("{},value={},version={}",zNode,newString(data),stat.getVersion()); } }catch(KeeperExceptione){ log.info("{}不存在",zNode); try{ //目的是添加Watcher zk.exists(zNode,true); }catch(KeeperExceptionex){ }catch(InterruptedExceptionex){ } }catch(InterruptedExceptione){ log.error("InterruptedException",e); } } @Override publicvoidrun(){ try{ synchronized(quitSemaphore){ quitSemaphore.wait(); log.info("{}被删除,退出",zNode); } }catch(InterruptedExceptione){ log.error("InterruptedException",e); } } /**主程序,代码中写死了Server地址和zNode名,也可以改成从args中读取*/ publicstaticvoidmain(String[]args){ StringhostPort="192.168.5.128:2181"; StringzNode="/watcher"; try{ newZooKeeperWatcher(hostPort,zNode).run(); }catch(Exceptione){ log.error("newZooKeeperExecutor()",e); } } }
做一个测试,应用启动后创建节点,修改多次节点,最后删除节点,日志输出如下:
10:13:31:979[INFO]-ZooKeeperWatcher.process(50)-event=WatchedEventstate:SyncConnectedtype:Nonepath:null 10:13:31:982[DEBUG]-ZooKeeperWatcher.log(201)- +Profiler[连接到ZooKeeper] |--elapsedtime[开始链接]210.193milliseconds. |--elapsedtime[等待连接成功的Event]9385.467milliseconds. |--Total[连接到ZooKeeper]9596.196milliseconds. 10:13:31:996[INFO]-ZooKeeperWatcher.readNodeData(84)-/watcher不存在 10:15:43:451[INFO]-ZooKeeperWatcher.process(50)-event=WatchedEventstate:SyncConnectedtype:NodeCreatedpath:/watcher 10:15:43:463[INFO]-ZooKeeperWatcher.readNodeData(81)-/watcher,value=hellozk00,version=0 10:15:50:906[INFO]-ZooKeeperWatcher.process(50)-event=WatchedEventstate:SyncConnectedtype:NodeDataChangedpath:/watcher 10:15:50:910[INFO]-ZooKeeperWatcher.readNodeData(81)-/watcher,value=hellozk01,version=1 10:15:56:004[INFO]-ZooKeeperWatcher.process(50)-event=WatchedEventstate:SyncConnectedtype:NodeDataChangedpath:/watcher 10:15:56:007[INFO]-ZooKeeperWatcher.readNodeData(81)-/watcher,value=hellozk02,version=2 10:16:00:246[INFO]-ZooKeeperWatcher.process(50)-event=WatchedEventstate:SyncConnectedtype:NodeDataChangedpath:/watcher 10:16:00:249[INFO]-ZooKeeperWatcher.readNodeData(81)-/watcher,value=hellozk03,version=3 10:16:06:399[INFO]-ZooKeeperWatcher.process(50)-event=WatchedEventstate:SyncConnectedtype:NodeDataChangedpath:/watcher 10:16:06:402[INFO]-ZooKeeperWatcher.readNodeData(81)-/watcher,value=hellozk10,version=4 10:16:10:217[INFO]-ZooKeeperWatcher.process(50)-event=WatchedEventstate:SyncConnectedtype:NodeDataChangedpath:/watcher 10:16:10:220[INFO]-ZooKeeperWatcher.readNodeData(81)-/watcher,value=hellozk11,version=5 10:16:14:444[INFO]-ZooKeeperWatcher.process(50)-event=WatchedEventstate:SyncConnectedtype:NodeDataChangedpath:/watcher 10:16:14:447[INFO]-ZooKeeperWatcher.readNodeData(81)-/watcher,value=hellozk12,version=6 10:16:20:118[INFO]-ZooKeeperWatcher.process(50)-event=WatchedEventstate:SyncConnectedtype:NodeDeletedpath:/watcher 10:16:20:118[INFO]-ZooKeeperWatcher.run(101)-/watcher被删除,退出
总结
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